Drug Prevents Breast Cancer In Some, Study Shows

Researchers have identified the first known drug that prevents breast cancer in some women in a study experts are calling a major breakthrough for the 185,000 women in the U.S. who get breast cancer each year.

A six-year study by the National Cancer Institute showed that the drug tamoxifen cut breast cancer rates nearly by half for women at risk for the disease, according to an account of the research published Sunday.

Although the drug had been shown to prevent tumors from recurring in breast cancer patients, this is the first time a study has shown benefits for women who have not had malignant tumors, according to Dr. Funmi Olopade, director of the Cancer Risk Clinic at the University of Chicago Hospitals.

"It is a dramatic result because breast cancer is the leading form of cancer for American women," said Olopade, whose clinic took part in the NCI research. "This is absolutely what we've been waiting for."

The results of the study are to be announced Monday by the cancer institute. The institute recently mailed letters describing the breakthrough to women who took part in the study, the Philadelphia Inquirer reported Sunday. The study's principal investigators declined to comment until the formal announcement, which had been scheduled for Wednesday until the newspaper's article.

Olopade cautioned that the study's data are still being analyzed and that tamoxifen might increase the risk of cancer of the uterine lining. The drug trial, involving 13,000 at-risk women, was temporarily suspended in 1994 to investigate four uterine cancer deaths that took place in a separate breast cancer study using tamoxifen.

Yet NCI investigators are encouraged enough by their results that they are informing women in the study's control group who were taking placebo pills that they could benefit from taking the drug. To do otherwise when the drug has demonstrated its effectiveness would be unethical, Olopade said.

The study gives the best evidence yet for any cancer-prevention drug. Researchers are studying chemicals that may reduce risks for prostate cancer and colon polyps, but none of them has shown as much promise as tamoxifen.

The trial was started in 1992. Tamoxifen is produced by Zeneca Pharmaceuticals of Wilmington, Del., a subsidiary of the British drugs company Zeneca Group Plc., and has been available since 1973.

Women at risk of getting the disease because of family history, precancerous breast lesions or age were randomly assigned to five years on either a placebo or tamoxifen.

According to the cancer institute, the drug reduced the rate of expected breast cancers in women to 1 in 130 from 1 in 236 during the study, the Inquirer reported.

Women who took part in the study responded enthusiastically to the letter.

"I'm just thrilled. Wow!" said Patricia Lorah, 45, of Reading, Pa., after receiving word. "My mother and grandmother died of breast cancer. This is almost overwhelming."

Although some aspects of its function are mysterious, tamoxifen appears to work by blocking receptors in the breast that use estrogen, a hormone that can cause breast cancer tumors to grow. The drug turns off cancerous cells in women who have tumors and prevents such cells from developing in women who are at risk.

Doctors had suspected tamoxifen would be useful as a preventative agent because of a study conducted 10 years ago that showed women who had cancer in just one breast had 47 percent less chance of getting a tumor in their other breast if they took the drug.

Tamoxifen acts differently on different parts of the body, a fact that can bring added risks or unique advantages.

While the drug reduces the effect of estrogen in women's breasts, it actually amplifies the hormone in the bones and other areas of the body. This can produce an increased risk of tumors in the uterine lining that feed on estrogen, but it also might give older women benefits such as decreased risk of heart disease and osteoporosis.

Olopade said the benefits are clear enough that women in high-risk groups would be well advised to get into a study on the effects of tamoxifen. Breast cancer claims 44,000 lives each year nationwide.

"We deal with women who have watched generations of their families die of breast cancer," Olopade said. "Now, we have a genetic test for those people, but up to now we haven't been able to do anything for them. Some have opted to have their breasts removed. Now, we have a chance to try something that may help."